Starting Out:

Prologues

I see a lot of people bad mouthing prologues, personally I like them when they're done right. A brief glimpse into the past or future is a great way to set the stage, but a random dump of information will make the reader lose interest.

Starting Chapter 1

A common writing mistake is starting the first chapter of a book with a character doing something mundane; taking a walk, waking up, driving... The first line needs to capture the reader's attention, and draw them in.Also, cliches like "It was a dark and stormy night" or "Once upon a time", while cute, are not a good idea unless you're trying to be funny. It's been overdone to the point that it looks amateurish.

Pacing

One thing to keep an eye on when writing is the progress or pacing of your story. If your plot is going too slow your readers will get bored, but if it goes too fast your reader may get lost or key information may be missed in the writing. And of course jumping between the two can straight up confuse your readers. Giving yourself some time before you reread your story can help with this so you can go over your work with renewed eyes. Though having a trusted friend or reader look over your work will also help you spot any inconsistencies in your story.

Developing Characters & Your World:

Character Appearances

First off, never information dump your character's appearance, it comes off as unskilled. It's better to work it into the story piece by piece. For example; Her earthy brown eyes blazed with anger. His dark long hair wiped in the wind.Also, try not to stereotype your character's ethnicity, it can come off looking racist and unprofessional. In a day where people are very careful to be politically correct, not being sensitive enough with some of your descriptions can turn a reader off. Though I imagine for some writers, that may be the point they're trying to make, so if you are aiming to stir up the reader, then be prepared with the possibility of bad reviews.

Your Story's Environment

The same goes for your world/town in your story as I stated about character appearances; don't information dump. It can cause the story to go off track, and make the reader lose interest. It's better to work it into a scene that can draw the reader in, and make it easier for them to experience your world:(For example)"The forest was dark with its thick leaves blocking out the dim light of pre-dawn. Ava’s bare feet stepped onto the surprisingly warm and soft mossy ground, it giving away slightly under her weight like a sponge." (Excerpt from "The Curse In The Woods)

Your Main Character

A perfect character is a boring character; I often see a lot of flawless heroes or heroines in books, and lose interest quickly. An unstoppable character is not only predictable, but lacks creativity. Let your main character grow; fail when they need to, and pick themselves up. Let them have fears and doubts, give them weaknesses. Give your character faults to struggle over, allowing your reader to relate and connect with your main character.

Character Names

I think we all have a tendency to overthink our characters' names, which is fine, but when you start naming your characters with names that are hard to pronounce/spell, it comes off as overly pretentious, and often downright annoying. A name shouldn't look like you randomly smashed your hand down on your keyboard. Often something simple is better.Also upon naming multiple characters try for names that start with different letters, and don't end the same:(For example) Brayden, Jayden, Kaiden.It can confuse readers, because often at a quick glance the mind will finish the name in one's head, and this can cause the reader to have to go back and reread a page or paragraph once they have become stumped. So much of this can be enough for someone to want to put a book down.Also when naming a character consider what nicknames they could be called by, it can add realism to your character, and is also a great way to show endearment between your characters.

Villains

Just as a perfect hero/heroine comes off as boring, so does a villain who's evil for the sake of being evil alone. Give them depth and background, give your readers a reason why the villain has turned to the dark side.My personal preference for a villain is either someone who starts off as a friend who over time becomes a hated fiend, or a bad guy whose lines blur to the point where they become a friend. A villain you can relate to is one that makes you think.

Killing Characters

There are a lot of reasons why to kill off a character, but unless you're writing a graphic horror, killing someone off for shock alone just won't do.

Good Reasons-Advancing a plot-Giving your character motivation-Adding realism to your theme (If you're writing about war then likely people will die.)-It shows the consequence to someone's actions

Bad Reasons-Wanting to make your reader sad-Trying to shock your reader-Being too lazy to give a character a proper write off

Give your readers a chance to get to know a character before you kill them off to allow maximum impact, and make sure there is a good reason behind their death, the more it's central to your plot the better. Eulogize your characters when you can to give their deaths meaning.